1. Field of the Invention
The present invention relates to a friction plate of a wet multi-disk clutch used in an automatic transmission, a friction engagement device or the like.
2. Description of the Related Art
FIG. 1 shows a basic structure of a wet multi-disk clutch. Reference numeral 1 denotes a snap ring; 2, a flange; 3, a separator plate; 4, a spline; 5, a drum connected to one rotation shaft; 6, an O-ring; 7, a core plate of a friction plate; 8, a hub connected to the other rotation shaft; 9, a piston for pressing the clutch; 10, a friction member fixed to each of opposite sides of the core plate; 11, an oil groove formed in the surface of the friction member; and 12, a lubricating oil supply port formed in the hub 8.
The friction plate 20 is constituted by the core plate 7 and the friction members 10.
When the piston 9 is pushed in a right direction (FIG. 1), the separator plates 3 and the friction plates 20 are pressed toward the flange 2, so that the rotation is transmitted between the drum 5 and the hub 8.
FIG. 2 shows a surface structure of a conventional friction plate 20, and a friction member 10 is fixed to each side or surface of a core plate 7. The friction member 10 has oil passages 21, extending therethrough from its inner peripheral surface 10a to its outer peripheral surface 10b, and oil grooves 11 which are open at their inner ends to the inner peripheral surface 10a, but does not extend to the outer peripheral surface 10b. The plates (disks) of the clutch are cooled by circulating oil. Simultaneously, when the clutch is to be disengaged, the plates are separated from one another by a pressure due to a centrifugal force of the oil in the oil grooves 11, thereby achieving a good clutch-disengaging effect.
In order to further enhance this clutch-disengaging effect, the width of the oil grooves 11 is larger than the width of the oil passages 21 so that the amount of the oil in each oil groove 11 can be increased.
FIG. 12 shows a graph in which the ordinate axis represents a torque (N m), and the abscissa axis represents a braking time (S (second)). A dot-and-dash line B indicates the conventional structure in which the oil grooves have a large width. Accordingly, the friction coefficient is low at the time of engagement of the clutch if the amount of the oil is too large. In contrast, if there is provided no oil groove, or if the oil grooves are too small, so that the amount of oil is small, an oil film runs short, so that the friction coefficient, obtained at the time of engagement of the clutch, becomes too high, as indicated by a broken line C in FIG. 12.
If the width of the oil grooves 11 is large, and the distal end of each oil groove 11 is disposed close to the outer peripheral surface 10b, then an outer peripheral portion 10c (see FIG. 2) has a narrow, elongate shape, and therefore there are encountered not only a problem that the strength is lowered but also a problem that heat is liable to be generated since these outer peripheral portions are narrow and less liable to dissipate heat.